Prior art closure failure detectors include stationary mold platen movement detectors which require relatively large forces to actuate. They typically employ strategically located microswitches external to the mold cavity and positioned relative to the stationary platen. They fail to prevent mold damage from multiple insert feeds or insert placement errors within the mold cavity.
Low pressure close circuits are standard on most injection molding machines. They provide for closing the mold under low pressure and measuring the resistance to closing in order to detect obstructions. These circuits do not normally provide for opening the press when an obstruction is detected and their level of sensitivity is limited by the requirement to overcome the normal resistances of the tool and of the press.
The use of spring-biased plungers for position detection is known in the prior art as exemplified by the literature such as "Hole Position and Orientation Finder," R. L. Kaftan and R. S. Shryock, IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 25, No. 7B, December 1982 (pp. 3911-3912). This reference discloses the use of a spring-loaded ball wiggler and plungers coupled to linear variable displacement transducers, the latter function to indicate linear displacement. The wiggler locates a hole. The reference, however, does not show nor suggest the detection of an insert as disclosed in this case.
The use of spring-biased plungers for molded part injection in association with injection molding devices is also known in the art as exemplified by "Plastic Molding Apparatus," A. T. Hardardt and F. B. Zykoff, IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 10, No. 11, April 1968 (pp. 1725-1726) which shows a spring-biased ejector pin associated with plastic molding of parts including inserts with the mold cavity. This reference shows a spring-loaded plunger for ejecting the molded item. It does not show nor suggest the claimed invention because it does not detect the presence of an incorrectly placed insert.
U.S. Pat. Nos. 3,726,625 (Rees) and 4,094,621 (Hehl) show arrangements of ejector pin configurations. U.S. Pat. No. 3,642,402 shows the use of pressure transducers in the injection nozzle and mold cavity, respectively. U.S. Pat. No. 3,647,309 shows the use of an ejector bar 36 coupled to a potentiometer 37 to detect the position of the mold elements. These references do not teach nor suggest the claimed invention because they do not show the detection of inserts placed in the mold cavity.
There are several types of mechanical mold protection devices available. Although the details of each may vary, the primary drawback of these systems is their level of sensitivity. The entire tool half must be displaced in order to detect the obstruction. This usually prevents major tool damage at the sacrifice of minor tooling details. They operate on the basic principle of physical displacement of one-half of the tool prior to completion of an electrical circuit by the closing of the mold halves. The two basic types are a spring-loaded fixed platen and a spring-loaded plate attached to a platen.